Magnetic and crystal structure of copper(II) fluoride

A powder sample of the monoclinic, weak ferromagnet CuF₂ was investigated by neutron diffraction. Using the profile method, the crystal structure was refined and the spin configuration determined. The layer type structure with planar quadratic fluorine coordination of Cu²⁺ (3d⁹) and the magnetic structure are remarkably similar to those of AgF₂. The spin configuration is however different from the magnetic structures of other 3d-fluorides; the magnetic unit cell is doubled with respect to the chemical cell (a_m = 2a, P2₁/c). The ordered magnetic saturation moment corresponds to quenched orbital momentum.     

The parallel susceptibility at 0 K of the double magnetic helix

The parallel susceptibility x^∥ at 0 K of a double magnetic helix of pitch angle ? in which two species of magnetic ions are acted on by unequal molecular fields is determined. The conditions under which x^∥ is equal to the 0 K perpendicular susceptibility x^⊥ calculated in the past are determined. Comparison is made with the powder susceptibility measurements performed on the orthorhombic compound La₂Fe_1.5Mn_0.5S₅ which displays a double magnetic helix up to T_N = 85 K.     

Far-infrared absorption of MgO: Fe2+ in magnetic fields

We have measured the far-infrared absorption of iron-doped MgO in the wavenumber region 10–200 cm^?1 and in magnetic fields up to 6 T. Absorption peaks found at 107.0 and 110.5 cm^?1 are assigned to magnetic dipole transitions between the spin-orbit Г_5g groundstate (J = 1) and the Г_3g, Г_4g excited states (J = 2) of the Fe²⁺ -ion at a cubic site. The observed magnetic field dependence shows that Г_4g is the higher excited level, so that the crystal field order of the levels is not changed by the reduction of the spin-orbit splitting attributed to a dynamic Jahn-Teller effect. An additional absorption peak at 33.4 cm^?1 is found to split in magnetic field.In iron-doped KMgF₃ absorption peaks at 52 and 87 cm^?1 that have previously been attributed to the same transitions of Fe²⁺ are found to remain unshifted and unsplit in magnetic fields up to 6 T.     

Effect of magnetic field on luminescence of MgS,CaS and CaO phosphors activated with Bi3+ ions

The magnetic field dependence of the intensity I(A₀) of the zero-phonon line of the ³A_1u → ¹A_1g emission band is measured at 4.2 K for MgS, CaS and CaO phosphors activated with Bi³⁺ ions. The increase in I(A₀) is proportional to the square of the external magnetic field. The results are compared with those for Pb²⁺-activated phosphors.     

Antiferromagnetic Ordering of Magnetic Clusters Units in Nb6F15

We have studied the magnetic cluster compound Nb₆F₁₅ which has an odd number of 15 valence electrons per (Nb₆F₁₂)³⁺ cluster core, as a function of temperature using nuclear magnetic resonance, magnetic susceptibility, electron magnetic resonance and neutron powder diffraction. Nuclear magnetic resonance of the ¹⁹F nuclei shows two lines corresponding to the apical F^a?a nucleus, and to the inner Fⁱ nuclei. The temperature dependence of the signal from the Fⁱ nuclei reveals an antiferromagnetic ordering at T < 5 K, with a hyperfine field of ~2 mT. Magnetic susceptibility exhibits a Curie–Weiss behavior with T _N ~5 K, and μ _eff ~1.57 μ_B close to the expected theoretical value for one unpaired electron (1.73 μ_B). Electron magnetic resonance linewidth shows a transition at 5 K. Upon cooling from 10 to 1.4 K, the neutron diffraction shows a decrease in the intensity of the low-angle diffuse scattering below Q ~0.27 Å^?1. This decrease is consistent with emergence of magnetic order of large magnetic objects (clusters). This study shows that Nb₆F₁₅ is paramagnetic at RT and undergoes a transition to antiferromagnetic order at 5 K. This unique antiferromagnetic ordering results from the interaction between magnetic spins delocalized over each entire (Nb₆F ₁₂ ⁱ )³⁺ cluster core, rather than the common magnetic ordering.     

Magnetic anisotropy of the organic conductors (TMTTF)2X

The anisotropy in the static magnetic susceptibility of some tetramethyltetrathiafulvalene salts (TMTTF)₂X (where X^- = PF^-₆, ClO^-₄, SCN^- and Br^-) has been investigated with a torque method between 3 K and 300 K for magnetic fields up to 11 kG. The experimental results show that the salts with X^- = SCN^- and Br^- become antiferromagnetic at about 8 and 13 K respectively, whereas for the two other salts above 1 kG no field dependence of the magnetic susceptibility is observed down to 3 K.     

Magnetic rotation observation of the C2b3Σg− ← a3Πu transition using a color center laser

The magnetic rotation observation of the C₂b³Σ_g^? ← a³Π_u Ballik-Ramsay system using a color center laser is reported. This is the first detection of this system in absorption. Three bands, 0 ← 1, 1 ← 2, and 2 ← 3, were identified in the spectral range 3650–4030 cm^?1. The last two bands were observed for the first time. In magnetic rotation many satellite lines (ΔN ≠ ΔJ) which would be very weak in normal absorption have been observed with intensity comparable to the main branch lines. This permits a slight improvement in the accuracy of some of the fine structure constants. A variety of lineshapes are observed for the various branches by magnetic rotation. Because the b³Σ_g^? fine structure is small, giving a partial overlap, the peak frequency of a magnetic rotation signal usually does not correspond to the center frequency of the normal absorption signal of that transition. A computer program has been written to predict magnetic rotation lineshapes and obtain the peak frequency displacements. Various observed and calculated lineshapes are displayed and compared.     

Structural and magnetic study of the Ti-doped barium hexaferrite ceramic samples: Theoretical and experimental results

We present a theoretical and experimental study of the structural and magnetic properties of M-type Ti⁴⁺-doped barium hexaferrite BaFe_{(12−(4/3)x)}Ti_xO₁₉ with x=0, 0.1, 0.2, 0.3, 0.5, 0.7 and 1.3. The XRD patterns and magnetic measurements show appreciable variations in the values of the saturation magnetization and the magnetic anisotropy field, H_an, with increasing Ti⁴⁺ content. We did not observe significant changes in the Lotgering factor along the (0 0 l) direction and in the texture coefficient, C_ex, which was estimated from the torque curves. The magnetic properties of these materials are explained by the combined effect of the coherent rotation of the magnetic domains and the replacements of Fe³⁺ by Ti⁴⁺ ions in the octahedral and tetrahedral sites. The influence of the Ti⁴⁺ content on the samples was studied theoretically by using a statistical phenomenological model. The main purpose of the model is to make preliminary predictions of the distribution of any dopant cation in the Fe³⁺ sites. As a result, we are able to analyze both structural and magnetic features of M-type barium hexaferrite.     

The magnetic structure of HoCo2Si2

We have carried out neutron diffraction on a HoCo₂Si₂ powder sample at 4.2 K. The magnetic structure of this compound is collinear antiferromagnetic with the holmium magnetic moments parallel to the c-axis of the crystal. The magnetic moment value of holmium is 9.85 μ_B. The magnetic space group is I4/mm'm' (Sh⁴¹⁰₁₂₈) k = 000 The ordering temperature is t_n = 12(1) K.     

Phase transitions in La1−x CaxMnO3−x/2 manganites

The crystal structure parameters and magnetic and electrical properties of La_1?x Ca_xMnO_3?x/2 reduced manganites with 0≤x≤0.5 are established. These investigations contribute to the understanding of magnetic interactions in manganites without Mn⁴⁺ ions. It is found that these manganites show a long-range antiferromagnetic order up to x=0.09 and transform into spin glasses at 0.09<x≤0.35. The compositions in the range 0.35<x≤0.5 show a strong increase in the spontaneous magnetization and critical point associated with the appearance of spontaneous magnetization and can therefore be viewed as inhomogenious ferromagnets. The magnetic and crystal structure peculiarities of La_0.5Ca_0.5MnO_2.75 are established by the neutron diffraction method. The strongly reduced samples show a large magnetoresistance below the point where the spontaneous magnetization develops. The magnetic phase diagram of La_1?x Ca_xMnO_3?x/2 is established by magnetization measurements. The magnetic behavior is interpreted assuming that the Mn³⁺-O-Mn³⁺ magnetic interaction is anisotropic (positive-negative) in the orbitally ordered phase and isotropic (positive) in the orbitally disordered phase. Introduction of the oxygen vacancies changes the magnetic interaction sign from positive to negative, thereby leading to a spin glass state in strongly reduced compounds. The results obtained reveal unusual features of strongly reduced manganites such as a large ferromagnetic component, a high magnetic ordering temperature, and a large magnetoresistance despite the absence of Mn³⁺-Mn⁴⁺ pairs. In order to explain these results, the oxygen vacancies are supposed to be ordered.     

Direct measurement of the nuclear magnetic dipole moment of Ho165 with the atomic beam magnetic resonance method

With an atomic beam magnetic resonance apparatus four rf transitions between different Zeeman levels of the⁴ I _15/2 ground state of Ho¹⁶⁵ have been measured in an external magnetic field of about 3000 Gauss. The interaction between the nuclear magnetic dipole moment and the external field could be deduced from these measurements. Because the magnetic field was measured by calibration transitions in K³⁹, Rb⁸⁵ and Rb⁸⁷, the following value could be determined for the nuclear magnetic dipole moment: μ _I (Ho¹⁶⁵)=4.094(44) μ _n (uncorrected for diamagnetic shielding). Thegj-factor of the ground state of Ho¹⁶⁵ was measured to begj(⁴ I _15/2, Ho¹⁶⁵)=1.1951445(40).     

Analysis of magnetic disaccommodation in La-Co-substituted strontium ferrites

M-type strontium ferrites substituted by La³⁺-Co²⁺(Sr_1−xLa_xFe_12−xCo_xO₁₉) were prepared by ceramic process. Effects of the substituted amount of La³⁺ and Co²⁺ on structure and magnetic properties of Sr_1−xLa_xFe_12−xCo_xO₁₉ compounds have systematically been investigated by X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and magnetic disaccommodation. In the measurement range from 80 to 500 K, the magnetic disaccommodation is represented by means of isochronal curves. It is well known that magnetic disaccommodation cannot be obviously found in the M-type of pure strontium ferrites. However, three peaks were observed in Sr_1−xLa_xFe_12−xCo_xO₁₉, and this behavior is explained in terms of the presence of Fe²⁺ cation and to the site occupation by the magnetic Co²⁺ ionic within the hexagonal structure.     

High-pressure effects on the crystal and magnetic structure of the Nd0.78Ba0.22CoO3 cobaltite

The crystal and magnetic structure of the Nd_0.78Ba_0.22CoO₃ cobaltite is studied by neutron diffraction at high pressures up to 4.2 GPa in the temperature range 10–300 K. The pressure dependences of structural parameters are obtained. Ferromagnetic ordering of the Co sublattice is observed at normal pressure below T _C ～ 140 K, and ferrimagnetic ordering of the Co and Nd sublattices with an antiparallel direction of magnetic moments appears at T _F ～ 40 K. The magnetic moment of Co and the temperature T _C change slightly under pressure, which points to the stability of the initial intermediate-spin (S = 1) state of Co³⁺ ions. This behavior differs considerably from the characteristic behavior of cobaltites that are close in chemical composition and structure and exhibit ferromagnetic ordering of only the Co sublattice. In these cobaltites, the magnetic moment of Co is substantially suppressed and T _C decreases under pressure, which is related to the change in the state of Co³⁺ ions from the intermediate spin state to the nonmagnetic low-spin state (S = 0). The interplay between the appearance of the magnetic interaction of the R-Co sublattices and the stability of the spin state of Co³⁺ ions in the Nd_0.78Ba_0.22CoO₃ cobaltite is discussed.     

Interaction between the magnetic moments of the 3d and the 4f electrons in manganite, probed by Ga substitution

The substitution of Ga for Mn in manganite Nd_0.6Dy_0.1Sr_0.3MnO₃ with a ferromagnetic (FM) ground state has been performed to study the influence of the Mn-sublattice magnetic ordering on the magnetic rare-earth sublattice. It is found that the substitution of Mn³⁺ with Ga³⁺ ions results in a sharp decrease of T_C, reflecting the reduction of the double-exchange interactions strength J_Mn-Mn. At the same time, a depinning effect of the rare-earth magnetic moment has been observed. This behavior unambiguously proves that the exchange interaction between Mn and rare-earth ions J_Mn-R strongly influences the rare-earth magnetic ordering at temperatures below T_C and stabilizes the rare-earth magnetic ground state.     

Magnetic circular dichroism of transition metal ions in solids-I. MgO:Cr3+

Absorption and magnetic circular dichroism (MCD) spectra of MgO: Cr³⁺ have been studied over the temperature range 5–300 °K and with magnetic fields up to 77 kG. A theory for intensity calculation using a weak field coupling scheme is discussed. Spin-forbidden transitions to ²E and ²T₁, are observed in MCD and are interpreted as magnetic dipole zero-phonon lines. The spin allowed bands ⁴T₂ and ⁴T₁ are found to be vibration-induced electric dipole transitions in which the t_1u lattice modes are the dominant contributors to the intensity.     

The antiferromagnetic structure of ErCo2Si2 by neutron diffraction

The magnetic structure of the tetragonal ErCo₂Si₂ compound is determined by neutron diffraction on powder sample at 4.2 K. The magnetic ordering is connected with a symmetry lowering, magnetic space group P_2s$\text{1}$ (Sh⁷₂)k = 000. The structure is collinear antiferromagnetic with the erbium magnetic moments making an angle of 56.2° with the c axis. The magnetic moment value for erbium is 6.75μ_B.     

Magnetic properties of Eu-Sc-Fe garnets studied with the Mössbauer effect

Magnetic properties of the garnet system Eu_3-ySc_2+yFe₃O₁₂ for 0 ? y ? 0.5 have been studied with ⁵⁷Fe and ¹⁵¹ Eu Mössbauer spectroscopy. The system is shown to have a ferrimagnetic structure. Both, the ordering temperatures and the hyperfine magnetic fields at the ⁵⁷Fe nuclei are found to increase with an increase in y. The iron magnetic moments at the octahedral and the tetrahedral sites are non-collinear. The average canting angles at these sites are determined and used for the calculation of the magnetic moments. Good agreement is obtained between the calculated and the experimental moment for the y = 0.0 sample. The determined magnetic properties are consistent with the recently proposed cation distribution in this system.     

Effect of electron irradiation on the paramagnetic state of La0.67Ca0.33MnO3

The effect of point defects on the magnetic properties of La_0.67Ca_0.33MnO₃ polycrystals and single crystals has been studied. The magnetic susceptibility χ _dc of the initial samples and samples irradiated by electrons to the maximum dose F = 9 × 10¹⁸ cm^?2 has been measured in the temperature region 80 K < T < 650 K. Local variations of Mn-O-Mn bond angles and lengths result in a nonmonotonic dose dependence of the Curie temperature T _C. At high doses of electron irradiation, F ≥ 5 × 10¹⁸ cm^?2, the temperature of the transition from the ferromagnetic to polaron state in a single crystal is found to increase. In the paramagnetic region close to T _C, ferromagnetically ordered polarons are observed to exist, while at T > 1.2T _C, localization of e _g electrons initiates formation of paramagnetic polarons with a higher magnetic moment. Electron irradiation stimulates persistence of magnetic polarons up to higher temperatures T > 2T _C.     

High-precision evaluation of the magnetic moment of the helion

NMR spectra of samples containing a mixture of hydrogen deuteride HD with pressure of about 80 atm and helium-3 with partial pressure of about 1 atm are analyzed. The ratio of the resonance frequencies of the nuclei, F(³He)/F(H₂), is determined to be 0.761786594(2), which is equal to the magnetic moment of the helion (bound in a helium atom) in the units of the magnetic moment of a proton (bound in molecular hydrogen). The uncertainty of two digits in the last place corresponds to a relative error of ??[F(³He)/F(H₂)] = 2.6 × 10^?9. The use of the known calculated data on the shielding of nuclei in the helium-3 atom (??(³He) = 59924(2) × 10^?9) and on the shielding of protons in hydrogen (??(H₂) = 26288(2) × 10^?9) yields a value of ??(³He)/?? _p = ?0.761812217(3) for the free magnetic moment of the helion in the units of the proton magnetic moment.     

Neutrino magnetic moment and shock-wave revival in a supernova explosion

The ν _L → ν _R → ν _L double conversion of the Dirac neutrino helicity is analyzed under supernova conditions, in which case the first stage is due to the interaction of the neutrino magnetic moment with plasma electrons and protons in the supernova core, while the second stage is caused by a resonance neutrino-spin flip in the magnetic field of the supernova envelope. It is shown that, if the neutrino has a magnetic moment in the range 10^?13 µ_B < µ _ν < 10^?12 µ_B and if a magnetic field of strength 10¹³ G exists between the neutrinosphere and the region of shock-wave stagnation, an additional energy on the order of 10⁵¹ erg, which is sufficient for stimulating a damped attenuated shock wave, can be injected in this region within the stagnation time.